Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $48.96   12.239%   $54.9522   $54.95   $54.95   $55.00  
  Purchase #2 $216.95   3.434%   $224.4001   $224.40   $224.40   $224.40  
  Purchase #3 $68.32   5.711%   $72.2218   $72.22   $72.20   $72.20  
  Purchase #4 $172.55   4.397%   $180.137   $180.14   $180.15   $180.10  
  Purchase #5 $86.74   8.264%   $93.9082   $93.91   $93.90   $93.90  
  Purchase #6 $164.58   5.588%   $173.7767   $173.78   $173.80   $173.80  
  Purchase #7 $144.43   3.347%   $149.2641   $149.26   $149.25   $149.30  
  7 purchase totals = $902.53       $948.6601   $948.66   $948.65   $948.70